The present invention relates to substrate processing. More specifically, the present invention relates to apparatus and methods for upgrading a substrate processing system. Some embodiments of the present invention are particularly useful for cleaning a chamber in a substrate processing system. However, other embodiments of the present invention also may be useful for etching or depositing films on a substrate processed in the chamber.
One of the primary steps in the fabrication of modern semiconductor devices is the formation of a layer, such as an oxide layer, on a substrate or wafer. As is well known, an oxide layer can be deposited by chemical vapor deposition (CVD). In a conventional thermal CVD process, reactive gases are supplied to the substrate surface where heat-induced chemical reactions take place to produce a desired film. In a conventional plasma-enhanced CVD (PECVD) process, reactant gases are disassociated by the application of energy such as radio frequency (RF) energy to a reaction zone proximate the substrate surface, thereby creating a plasma of highly reactive species to produce the desired film.
During CVD processing, reactive gases released inside the processing chamber form layers such as silicon oxides or nitrides on the surface of a substrate being processed. However, deposition of undesired oxide or nitride residue can occur elsewhere in the CVD apparatus, such as in the area between the gas mixing block and gas distribution manifold, in or around the exhaust channel, and on the walls of the processing chamber during such CVD processes. Over time, failure to clean the residue from the CVD apparatus often results in degraded, unreliable processes and defective wafers. Typically, two types of cleaning procedures are used. Occurring between the processing of every wafer or every n wafers, the first cleaning procedure uses an etchant gas, optionally formed with a plasma, to remove residue from chamber walls and other areas. Occurring far less frequently than the first cleaning procedure, the second cleaning procedure involves opening the processing chamber and physically wiping the entire reactor--including the chamber walls, exhaust and other areas having accumulated residue--with a special cloth and cleaning fluids. Without these frequent cleaning procedures, impurities from the residue built up in the CVD apparatus can migrate onto the wafer. The problem of impurities causing damage to the devices on the substrate is of particular concern with increasingly small feature dimensions in modern devices. Thus, properly cleaning CVD apparatus is important for the smooth operation of substrate processing, improved device yield and better product performance.
Although effective chamber cleaning may be performed with conventional CVD apparatus, efficiency problems are encountered. Some conventional CVD apparatus, such as the parallel-plate capacitively coupled RF plasma CVD apparatus, have a processing chamber with integral RF sources that produce the plasma in situ. Thus, the first cleaning procedure may be performed without opening the processing chamber in such CVD apparatus. However, the plasma produced in the processing chamber may not be sufficient to clean all the areas with residue build-up, unless the duration of the cleaning operation is increased to compensate for the lower etch rate. However, this adversely affects substrate throughput and overall efficiency. Moreover, use of the RF plasma also causes ion bombardment of the metallic parts of the CVD apparatus, causing physical damage to the gas distribution manifold and to the inside chamber walls, and possibly leading to metal contamination problems.
Other conventional CVD apparatus having a separate processing chamber connected to a bulky, somewhat fragile remote microwave plasma system also introduce different efficiency problems. In such CVD apparatus, the entire remote plasma source, which includes a plasma applicator tube, a magnetron with power source, isolator, ultra-violet (UV) lamp, bulky waveguide and tuning assembly, is positioned over and securely fastened onto the lid of the processing chamber and extends down the side to the base of the chamber. Because the high breakdown efficiency with a microwave plasma results in a higher etch rate (on the order of about 2 .mu.m/min) than is obtained with a capacitive RF plasma, these remote microwave plasma systems provide a plasma that can efficiently and adequately clean the residue without ion bombardment. Such remote microwave plasma systems typically utilize expensive, high wattage, continuous wave (CW) power supplies that power magnetrons to provide between about 2.5 to 6 kilowatts (kW) of microwave power. However, performing the second cleaning procedure (which is a serious, albeit necessary, interruption in the manufacturing of substrates) with these CVD apparatus may be even more time-consuming because the bulky, fragile remote microwave plasma system must be carefully removed from the top of the chamber, which needs to be opened for manual cleaning. In particular, the entire remote plasma source assembly needs to be unfastened near the top of the processing chamber as well as near the base of the chamber. Then the assembly needs to be carefully extracted from the processing chamber, without damaging any part of the entire assembly, while cleaning occurs. Often a difficult and unwieldy process, removing the bulky remote source further increases the total time required to perform preventive maintenance cleaning, and risks damaging the remote plasma source, which may be expensive to repair. Further, removing the bulky remote source involves removing the extensive waveguide system, and replacing the waveguide system requires a time-consuming quality control process to check for microwave leakage.
In addition to the above-described efficiency problems, use of CVD apparatus with conventional remote microwave plasma systems also introduces other problems including increased maintenance costs. In particular, these conventional microwave plasma systems, which have assemblies with configurations that require liquid cooling of the applicator tube, produce plasma in a relatively small physical space in the applicator tube (for example, a two-inch lengthwise section of an applicator tube having a 1 inch diameter) and thus require high power density, high cost, direct current (DC) microwave power supplies in order to obtain a high microwave coupling efficiency. The operation of such high power density power supplies thus results in increased utility bills. In addition, the plasma formed in this small space with magnetrons using such high power supplies has a high plasma density and the requisite cooling requirements of configurations often necessitate the use of a water-cooled or other liquid-cooled system. Typically, liquid-cooled systems are more expensive and have high maintenance costs, for example, providing coolant fluids. Also, liquid-cooled systems often suffer from leakage problems. Such leakage may lead to corrosion of the equipment, which may cause a degradation in the quality of the processed substrates. Moreover, frequent cleaning or even replacement of parts in the plasma source may be required due to the corrosion damage. In cases of extreme corrosion, the entire remote plasma source equipment or perhaps other equipment close to the remote plasma source may need to be replaced. Such cleaning and/or replacement procedures further interrupt the manufacturing of substrates. These types of delays have a negative economic impact on the manufacturer. Also, processing chamber maintenance for liquid-cooled systems requires removal of the plasma source, a time-consuming and involved process, that increases the total time manufacturing is interrupted.
From the above, it can be seen that it is desirable to have a modular, conveniently sized remote microwave plasma source assembly that permits economic and efficient cleaning of the CVD apparatus economically and efficiently, and that is easily handled and removable to reduce the amount of time needed for preventive maintenance cleaning. It is also desirable to provide a relatively inexpensive, yet high quality, remote microwave plasma source that may be a removable addition to or a retrofit of existing CVD apparatus, in order to upgrade performance of the CVD apparatus for improved cleaning ability while minimizing costs.